posted by cortez .
why is the 4% important to the CI? Please give an example.
What 4%? If you are talking about the difference between a CI of 95% and 99%, the latter is more likely to include the true mean. It depends on how much of a risk you want to take in terms of estimating the mean.
Of course, the larger your n, the more accurate your estimate of the mean, until finally your have measured the whole population and are certain of the mean.